Typically, in a passenger aircraft, air being supplied to the cabin for the comfort of the passengers is conventionally obtained from air bled from the engine. This type of system has proven inefficient for certain types of aircraft engines Therefore, other systems have been proposed.
One proposed alternative to the conventional system is to provide an air compressor driven by an engine drive shaft. Although such a system would be advantageous, the system must satisfy a number of requirements.
Primarily, such a system must be able to make use of a varying rotational speed supplied by the drive shaft of the aircraft engine. Also, the system must fit within the space provided within the engine installation and maintain required cabin air flow and pressure and supply a controlled amount of air to the cabin regardless of engine speed.
As is well-known, the rotational speed of an engine drive shaft varies over a wide rotational speed range. Thus, an air compressor coupled directly to the drive shaft of an engine would suffer from the disadvantage of having applied thereto a varying rotational speed. The varying rotational speed applied to the compressor makes it nearly impossible to maintain a required airflow and pressure in the cabin of an aircraft as demanded by varying altitude and air speed. Additional apparatus is necessary in order to cause a compressor being driven by a varying rotational speed to maintain a require airflow and pressure in the cabin of the aircraft
The additional apparatus may take the form of apparatus for modifying the flow of air output by the compressor or apparatus for converting the varying rotational speed into a controlled rotational speed by the use of a variable speed transmission.
For example, an air conditioning apparatus is disclosed by U.S. Pat. No. 2,697,917. The apparatus disclosed in U.S. Pat. No. 2,697,917 provides an air conditioning apparatus of an aircraft having an air modulating apparatus for modulating the air from an air pump so as to maintain the required pressure and temperature in the enclosure of the aircraft. Although U.S. Pat. No. 2,697,917 provides for the modulation of air being supplied to an enclosure of an aircraft in order to regulate the pressure and temperature in the enclosure. Such a system does not attempt to modify the varying rotational speed being applied to the air pump. Thus, the compressor must operate at very high speeds and power levels when the speed of the aircraft engine is near maximum.
U.S. Pat. No. 2,441,779 discloses a rate of flow regulator for controlling the amount of air delivered to a pressurized cabin of an aircraft. Particularly, U.S. Pat. No. 2,441,779 provides differential gearing and a pump for controlling the speed of a supercharger to provide certain air flow rates irrespective of the speed of the engine. The pump in U.S. Pat. No. 2,441,779 serves as a brake to control the speed of the supercharger.
U.S. Pat. No. 2,390,487 discloses a flow regulating system for controlling the rate of flow of air to a supercharger which outputs air to an aircraft cabin. The flow regulating system disclosed by U.S. Pat. No. 2,390,487 suffers from the disadvantage of a hydraulic pump serving as the brake to control the rotational speed of the compressor.
U.S. Pat. No. 4,523,517 discloses a system which provides an electric motor to drive a compressor. The electric motor in U.S. Pat. No. 4,523,517 operates by making use of power generated by electric generators driven by the aircraft engine. The system disclosed by U.S. Pat. No. 4,523,517 suffers from the disadvantage of the rotational speed being output by the electric motor increasing when the aircraft engine speed increases.
Further examples of variable speed compressor drive systems are disclosed by U.S. Pat. Nos. 2,452,704 and 2,539,571. However, such systems do not integrate the compressor with the rest of the system and do not use the more efficient split path power drive concept.